Efforts directed at improving air quality and increasing energy production from renewable resources have resulted in renewed interest in alternative fuels, such as ethanol and butanol, that might replace gasoline and diesel fuel, or be used as additives in gasoline and diesel fuel.
Methods for producing isobutanol from methanol and other alcohols, particularly ethanol, are known. It is known that isobutanol can be prepared by condensation of ethanol and methanol over basic catalysts at high temperature using the so-called “Guerbet Reaction.” See for example, J. Logsdon in Kirk-Othmer Encyclopedia of Chemical Technology, John Wiley and Sons, Inc., New York, 2001.
In addition, U.S. Pat. No. 5,300,695, assigned to Amoco Corp., discloses processes in which an alcohol having X carbon atoms is reacted over an L-type zeolite catalyst to produce a higher molecular weight alcohol. In some embodiments, a first alcohol having X carbon atoms is condensed with a second alcohol having Y carbon atoms to produce an alcohol having X+Y carbons. In one specific embodiment, ethanol and methanol are used to produce isobutanol using a potassium L-type zeolite.
J. I. DiCosimo, et al., in Journal of Catalysis (2000), 190(2), 261-275, describe the effect of composition and surface properties on alcohol-coupling reactions using MgyAlOx catalysts for alcohol reactions.
Carlini et al. describe a catalytic reaction of methanol with n-propanol to produce isobutyl alcohol. The involved catalyst is a calcined hydrotalcite in combination with copper chromite. See C. Carlini et al, Journal of Molecular Catalysis A: Chemical (2005), 232 (1-2) 13-20. See also C. Carlini, Journal of Molecular Catalysis A: Chemical (2004), 220 (2), 215-220, in which the catalyst is a mixture of a hydrotalcite with palladium, nickel, rhodium or copper, with the mixture being calcined at 500° C.
Hydrotalcites are layered, double hydroxides of the general formula(M2+1-xM3+x(OH)2)(An−x/n)●yH2OThe M2+ ions can be a variety of divalent cations (e.g., Mg, Ni, Pt, Pd, Zn, Co, Fe, Cu) and the M3+ ions can be trivalent Al, Fe or Cr. Some hydrotalcites are described by V. K. Diez, C. R. Apesteguia, and J. I. DiCosimo (Latin American Applied Research, 33, 79-86 (2003)) and N. N. Das and S. C. Srivastava (Bull. Mater. Sci. 25, (4), 283-289 (2002)).
It has been found that partially or fully thermally decomposed hydrotalcites, particularly those that incorporate transition metals, are catalysts that are effective for the conversion of ethanol plus methanol to a reaction product that comprises (i.e., contains, among other things) isobutanol.